No abstract

A new ten-locus STR (short tandem repeat) profiling system was recently introduced into casework by the Forensic Science Service (FSS) and statistical analyses are described here based on data collected using this new system for the three major racial groups of the UK: Caucasian. Afro-Caribbean and Asian (of Indo-Pakistani descent). Allele distributions are compared and the FSS position with regard to routine significance testing of DNA frequency databases is discussed. An investigation of match probability calculations is carried out and the consequent analyses are shown to provide support for proposed changes in how the FSS reports DNA results when very small match probabilities are involved.

No abstract

The utilization of DNA evidence in cases of forensic identi®cation has become widespread over the last few years. The strength of this evidence against an individual standing trial is typically presented in court in the form of a likelihood ratio (LR) or its reciprocal (the pro®le match probability). The value of this LR will vary according to the nature of the genetic relationship between the accused and other possible perpetrators of the crime in the population. This paper develops ideas and methods for analysing data and evaluating LRs when the evidence is based on short tandem repeat pro®les, with special emphasis placed on a Bayesian approach. These are then applied in the context of a particular quadruplex pro®ling system used for routine case-work by the UK Forensic Science Service.

The paper provides a review of current issues relating to the use of DNA profiling in forensic science. A short historical section gives the main statistical milestones that occurred during a rapid development of DNA technology and operational uses. Greater detail is then provided for interpretation issues involving STR DNA profiles, including:-methods that take account of population substructure in DNA calculations; -parallel work carried out by the US National Research Council; -the move away from multiple independence testing in favour of experiments that demonstrate the robustness of casework procedures; -the questionable practice of source attribution 'with reasonable scientific certainty'; -the effect on the interpretation of profiles obtained under increasingly sensitive techniques, the LCN technique in particular; -the use of DNA profiles as an intelligence tool; -the interpretation of DNA mixtures.Experience of presenting DNA evidence within UK courts is also discussed. The paper then summarises a generic interpretation framework based on the concept of likelihood ratio within a hierarchy of propositions. Finally the use of Bayesian networks to interpret DNA evidence is reviewed.